Geraint Thomas dug deep to retain the overall lead at the Tour Down Under as Tom Jelte Slagter took the win on stage three.

Thomas and Team Sky were able to defend the leader's Ochre jersey on a brutally tough stage in the Australian heat on an undulating circuit around Stirling.

At the finish there was a surprise winner in Slagter (Blanco Cycling) who held off his rivals on the uphill drag to the line.

Thomas narrowly missed out on bonus seconds at the line with fourth, yet maintained his five-second lead while Matthew Goss (Orica-GreenEDGE) and Philippe Gilbert (BMC Racing) rounded out the podium on the day.

In temperatures of up to 38 degrees Celsius Team Sky spent the majority of the stage on the front, an impressive force which was put to the test by numerous attacks.

After the finish leader Thomas said: "It was pretty tough out there. A lot of guys started attacking us from three laps out so the boys had to ride really hard. They did an incredible job today. They set a fast tempo and I can't thank them enough.

"In the final [Mathew] Hayman was with me until about two kilometres to go and then after that I just had to follow the wheels. I couldn't manage a podium finish which would have been nice to get a few more seconds but it was a tough day so it's mission accomplished I guess."

With a new rival emerging in the now second-placed Slagter Thomas added: "It's always going to be seconds in it and I think it's all going to come down to a big duel on Willunga on Sunday."

139km in the heat lay ahead as the riders left Unley for what many were describing as the toughest test of the race with six laps of a heavy stage around Stirling on the agenda.

The first job of the day for Team Sky was to control a surging peloton as the stage got under way, the race heading up the steep Mount Barker Road to the first categorised climb.

A group of 23 riders broke clear early on but in the end it was a two-man break of namesakes William Clarke (Argos-Shimano) and Simon Clarke (Orica-GreenEDGE) who went clear.

Thomas and Team Sky were alert at the first sprint point in Heathfield as Thomas nipped out to take third place and a single second to add to his race lead.

With the gap spinning out to 3:25 Team Sky set about pegging the duo, Bernhard Eisel again grinding away on the front for the third day running before the rest of the team took up the baton.

With 50km to go the race received a shake-up as numerous attacks tried to fire clear from the peloton, forcing Team Sky to re-double their efforts.

With help finally arriving from Lotto-Belisol a dangerous late move from Tiago Machado (RadioShack-Leopard) was snuffed out but at the line it was Slagter who claimed a breakthrough victory.

Thomas told Eurosport: "The boys had to ride really hard, they did an incredible job today. It was a tough day so that's mission accomplished I guess."

Slagter said of his stage win: "It's incredible, I can't believe it.

"I saw on the screen that I was the first one. I thought they were coming... but I was the strongest, it's incredible."